I had the same issue when we went earlier this month. I declared I would eat as healthy of meals as I could and then indulge on desserts (they are my favorite : ) ). So here were my favorites:
Columbia Harbor in MK-lighthouse sandwich was very good, I got it with a light strawberry yoplait. (I think this was my favorite CS)
I didn't go but I heard Sunshine Seasons in Epcot has lots of delicious and healthy options (veggie flatbread, goat cheese salad).
Starring Rolls was supposed to have a veggie sandwich, and I went at 12:00 and they were already out. So I wouldn't count on that...but they had some pretty mediocre sushi. (BUT TRY THE CUPCAKES!!)
Yak and Yeti in AK had a grilled chicken breast with tamarind sauce that came with veggies and jasmine rice (I subbed in brown rice with no problem)...this was a very delicious meal that I recommend.
Tokyo Dining in Epcot has good sushi, if you are into that.
Wolfgang Puck cafe had a very delicious spinach salad with apples, walnuts and cheese (you can get a meat on top to make it a full meal on you
disney dining plan).
Otherwise, almost everywhere CS and TS has some type of basic salad with grilled chicken on top. But beware caesar salads, the dressing is full of fat!
I hope this helps, good luck on your healthy endeavors! But make sure you enjoy all the yummy goodies afterwards : ))))